Why is it bad to not let a new engine idle for a long time?

[pigeon]

As the title states, why is it bad to let a new engine idle for a long time?
I've heard different reasons from different people, but never heard a logical explanation.... does anyone know?

[Tazman2]

For the same reason your not suppose to keep the same rpms/speed when breaking in a engine. It needs different loads/rpms, etc. to break in properly. Past that i can't explain it!

[photoeye0]

I don't know for sure ether, but I do know not to do it.

My dad just let his new Buell motor "idle brake in" and it started burnin' oil by the end of the summer.

Just a FYI.